Thermal transfer image-receiving sheet

ABSTRACT

There is provided a thermal transfer image-receiving sheet comprising: a substrate sheet; and an image-receiving layer provided on one side of the substrate sheet, the image-receiving layer comprising a copolymer, having an average degree of polymerization of 800 to 2000, of at least vinyl chloride and vinyl acetate as main comonomers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a thermal transfer image-receiving sheetwhich, in use, is laminated onto a thermal transfer sheet. Moreparticularly, this invention relates to a thermal transferimage-receiving sheet which can provide a very sharp, highly transparentimage independently of environmental conditions such as temperature andhumidity.

2. Background Art

Various thermal transfer recording systems are known in the art. Amongthem, a thermal dye transfer system, wherein a thermal transfer sheetcomprising a support, such as a polyester film, bearing a thermaltransfer layer containing a sublimable dye is heated by means of heatingmedium, such as a thermal head or a laser beam, to form an image on arecording medium, have recently drawn attention and utilized asinformation recording means in various fields.

This thermal dye transfer system can form, in very short time, afull-color image having excellent halftone reproduction and gradationand a quality comparable to that of full-color photographic images.

Further, according to this system, since a resin constituting theimage-receiving layer is dyed with a dye to form an image, the formedimage advantageously has high sharpness and excellent transparency and,hence, has been extensively used in the preparation of transparentoriginals for projectors, such as overhead projectors (hereinafterabbreviated to "OHP").

The conventional image-receiving sheet for OHP comprises an about 100μm-thick transparent substrate sheet of polyethylene terephthalate(hereinafter often abbreviated to "PET") bearing an image-receivinglayer on one side thereof and a back side layer on the other sidethereof.

The image-receiving layer functions to receive a sublimable dye beingtransferred from a thermal transfer sheet and to hold the formed imageand is formed of a thermoplastic resin, for example, a saturatedpolyester resin, a vinyl chloride/vinyl acetate copolymer, or apolycarbonate resin. If necessary, an intermediate layer is provided onthe image-receiving layer side of the substrate.

For example, a layer for imparting a cushioning property in the case ofa highly rigid substrate, such as PET, and a layer for imparting anantistatic property are optionally provided as the intermediate layer.

The back side layer functions to prevent curling and to improve theslipperliness of the image-receiving sheet and is formed by coating acomposition containing a binder, such as an acrylic resin, with anorganic filler, such as a fluororesin or a polyamide rein, or aninorganic filler, such as silica, incorporated therein.

On the other hand, in the case of the so-called "standard type thermaltransfer image-receiving sheet," the image-receiving sheet is viewed orused by taking advantage of reflected light rather than transmittedlight. The construction of this standard type thermal transferimage-receiving sheet is substantially the same as that of the abovethermal transfer image-receiving sheet, except that, the substrate isconstituted by an opaque material, for example, white PET, foamed PET,other plastic sheet, natural paper, synthetic paper, or a laminatethereof.

Some vinyl chloride/vinyl acetate copolymer resins having a relativelylow degree of polymerization have hitherto been used as one of resinsfor image-receiving layer of the conventional thermal transferimage-receiving sheet and offered good printing performance.Commercially available vinyl chloride/vinyl acetate copolymer resins forsuch applications include, for example, resins available under the tradename designations S-lec A, S-lec C, and S-lec M (manufactured by SekisuiChemical Co., Ltd.), Vinylight VYHH, Vinylight VYHD, Vinylight VYNS,Vinylight VMCH, Vinylight VMCC, Vinylight VMCA, Vinylight VAGH, andVinylight VAGD (manufactured by Union Carbide Corporation, U.S.A.), andDenka Vinyl #1000 AKT, Denka Vinyl #1000 AS, Denka Vinyl #1000 MT, DenkaVinyl #1000 MT2, Denka Vinyl #1000 GK, Denka Vinyl #1000 GKT, DenkaVinyl #1000 CS, Denka Vinyl #1000 CSK, Denka Vinyl #1000 LT3, and DenkaVinyl #1000 D (manufactured by Denki Kagaku Kogyo K.K.). These resinshave an average degree of polymerization of about 200 to 700. Such vinylchloride/vinyl acetate copolymer resins having a relatively low degreeof polymerization can be easily dissolved in an organic solvent, and, byvirtue of this feature, have been used in various applications includingbase resins of adhesives and paints. Further, since such resins havesuitable receptivity to dyes, they, either alone or as a mixture thereofwith a polyester resin are, in many cases, used as a base resin of animage-receiving layer in an image-receiving sheet used with a thermaldye transfer sheet. However, the conventional thermal transferimage-receiving sheets using the above vinyl chloride/vinyl acetatecopolymer resins having a relatively low degree of polymerization as theresin for constituting the image-receiving layer have the followingproblems.

For example, in the case of an image-receiving sheet for OHP, a highdensity is required of a transparent print in order to providesatisfactory dynamic range (three-dimensional effect and design) in theprojection of the image, and, for this reason, considerable energy isapplied to a high-density print area. The surface of the image-receivinglayer is subjected to damage by the heat and consequently roughened. Theroughening results in scattering of light which is transmitted orreflected at the time of projection through OHP, so that the projectedimage is blackish.

On the other hand, in the case of the standard type image-receivingsheet, light is unfavorably reflected from the roughened surface, posingproblems including that only a part of the image becomes matte and thedensity of a portion where high energy has been applied in order toprovide high density becomes low due to the roughening.

For the above reason, in the case of image-receiving sheets for OHP orof the standard type, satisfactory energy cannot be applied from theviewpoint of avoiding this problem of roughening, making it impossibleto provide necessary density.

Furthermore, the conventional image-receiving sheets have the followingproblem associated with feed into a thermal transfer printer.Specifically, when a plurality of sheets of the image-receiving sheetare put on top of one another within a sheet cassette and fed one by oneby means of a pickup roll into the printer, friction occurs between theback side layer of one sheet and the image-receiving surface of anothersheet, causing the image-receiving surface to be scratched. Thisdeteriorates the appearance of the sheet, and, in addition, at the timeof printing, causes abnormal transfer, which is such an unfavorablephenomenon that the dye layer of the thermal transfer sheet, togetherwith a binder, is transferred onto the surface of the image-receivinglayer, or, at the time of projection of the image through OHP, causesthe scratch as well as the image to be projected as a blackish image,making it impossible to provide a desired image.

When the substrate is made of a rigid material, such as PET, the problemof scratching often occurs not only at the time of feed of theimage-receiving sheet into the printer, but also in the course of beingcarried within the printer due to friction between the sheet and aninternal mechanism(s).

Furthermore, the conventional image-receiving sheet has an additionaldrawback that it is likely to be curled by heat or pressure applied atthe time of printing by means of a thermal transfer printer, by heatfrom light source of OHP, or by the temperature of an environment underwhich the image-receiving sheet is stored.

Furthermore, during the preparation of the thermal transferimage-receiving sheet, static electricity created in the thermaltransfer image-receiving sheet causes carrying troubles and depositionof dust. In addition, the static electricity poses a problem of carryingtroubles within a thermal transfer printer, for example, double feed atthe time of feed of the image-receiving sheet into the printer.

The present invention has been made with a view to solving the aboveproblems of the prior art, and an object of the present invention is toprovide a thermal transfer image-receiving sheet which can preventroughening of the surface of the image-receiving layer in itshigh-energy printing area and creates no scratch in the image-receivinglayer even in the case of friction between a plurality of sheets of theimage-receiving sheet at the time of feed into a printer.

SUMMARY OF THE INVENTION

According to the present invention, the above object can be attained bya thermal transfer image-receiving sheet comprising: a substrate sheet;and an image-receiving layer provided on one side of the substratesheet, the image-receiving layer comprising a copolymer, having anaverage degree of polymerization of 800 to 2000, of at least vinylchloride and vinyl acetate as main comonomers. According to onepreferred embodiment of the present invention, the coverage of theimage-receiving layer is 0.5 to 4.0 g/m² on a dry weight basis.According to another preferred embodiment of the present invention, thethermal transfer image-receiving sheet further comprises a back sidelayer provided on the other side of the substrate sheet, the back sidelayer being formed of a composition comprising an acrylic polyol andfine particles of an organic material. According to a further preferredembodiment of the present invention, the thermal transferimage-receiving sheet further comprises an intermediate layer, having anantistatic property, between the substrate sheet and the image-receivinglayer.

The substrate sheet is preferably a transparent sheet. Further,preferably, at least one side of the substrate sheet has been subjectedto adhesiveness-improving treatment and/or antistatic treatment.

The present invention can realize a thermal transfer image-receivingsheet which can prevent roughening of the surface of the image-receivinglayer in its high-energy printing area and, hence, can be used as an OHPsheet free from blackening of high-density area at the time ofprojection through OHP, and, in the case of the standard typeimage-receiving sheet, can prevent only a high-density area frombecoming matte.

In the conventional thermal transfer image-receiving sheet, satisfactoryenergy cannot be applied in order to avoid blackening or matting of theimage attributable to the roughening of the surface of theimage-receiving layer, making it impossible to provide necessary imagedensity. By contrast, according to the thermal transfer image-receivingsheet of the present invention, the application of satisfactory energyposes no matte problem, offering a contemplated good image. Further, thethermal transfer image-receiving sheet of the present invention canwithstand friction between a plurality of sheets of the image-receivingsheet at the time of feed of the sheet into a printer, enablingscratching of the image-receiving layer to be prevented. Therefore,unlike the conventional thermal transfer image-receiving sheet, thethermal transfer image-receiving sheet of the present invention canavoid troubles such as abnormal transfer, caused by the presence ofscratch, and has high reliability.

Further, the provision of an intermediate layer, having an antistaticproperty, between the image-receiving layer and the substrate sheet andantistatic treatment of the outermost surface of the thermal transferimage-receiving sheet can improve the carriability of the thermaltransfer image-receiving sheet within a thermal transfer printer underany environment.

DETAILED DESCRIPTION OF THE INVENTION

The thermal transfer image-receiving sheet of the present invention willbe described in detail.

<Substrate sheet>

The substrate sheet functions to support an image-receiving layer and,preferably, is not deformed by heat applied at the time of thermaltransfer and has mechanical strength high enough to cause no troublewhen handled in a printer or the like.

Materials for constituting the substrate sheet is not particularlylimited, and examples thereof include films of various plastics, forexample, polyesters, polyacrylates, polycarbonates, polyurethane,polyimides, polyetherimides, cellulose derivatives, polyethylene,ethylene/vinyl acetate copolymer, polypropylene, polystyrene,polyacrylonitrile, polyvinyl chloride, polyvinylidene chloride,polyvinyl alcohol, polyvinyl butyral, nylon, polyetheretherketone,polysulfone, polyethersulfone, tetrafluoroethylene/perfluoroalkyl vinylether copolymer, polyvinyl fluoride, tetrafluoroethylene/ethylenecopolymer, tetrafluoroethylene/hexafluoropropylene copolymer,polychlorotrifluoroethylene, and polyvinylidene fluoride. Among them,transparent sheets may be used as the substrate of the thermal transferimage-receiving sheet for OHP applications. In the case of the standardtype thermal transfer image-receiving sheet, it is possible to use,besides the above films, a white opaque film, prepared by adding a whitepigment or a filler to the above synthetic resin and forming the mixtureinto a sheet, and a foamed sheet. Further, various types of papers, suchas capacitor paper, glassine paper, parchment paper, synthetic papers(such as polyolefin and polystyrene papers), wood free paper, art paper,coat paper, cast coated paper, paper impregnated with a synthetic resinor an emulsion, paper impregnated with a synthetic rubber latex, paperwith a synthetic resin internally added thereto, and cellulose fiberpaper.

Furthermore, laminates of any combination of the above substrate sheetsmay also be used. Representative examples of the laminate include alaminate of cellulose fiber paper and synthetic paper and a laminate ofcellulose fiber paper and a synthetic paper of a plastic film.

Furthermore, at least one side of the above substrate sheets may havebeen subjected to treatment for improving the adhesion.

Preferably, the substrate sheet has a surface resistivity of not morethan 1.0×10¹² Ω□ under an environment of temperature 20° C. and relativehumidity 50%. Such a substrate sheet may be selected from the abovematerials. Alternatively, the materials may be subjected to antistatictreatment to bring the surface resistivity to the above value. The useof the substrate sheet having the above surface resistivity can preventtroubles caused by static electricity during the production of theimage-receiving sheet and, at the same time, can enhance the effect ofan antistatic agent, described below, coated on the image-receivingsurface and/or the back surface of the thermal transfer image-receivingsheet.

The thickness of the substrate sheet is generally about 3 to 300 μm. It,however, is preferably 75 to 175 μm from the viewpoint of mechanicalproperties and other properties. If the substrate sheet has pooradhesion to a layer provided thereon, the surface thereof may besubjected to adhesiveness-improving treatment or corona dischargetreatment.

<Image-receiving layer>

According to the thermal transfer image-receiving sheet of the presentinvention, the image-receiving layer comprises a copolymer, having anaverage degree of polymerization of 800 to 2000, of at least vinylchloride and vinyl acetate as main comonomers.

Other monomers which may be used as other comonomer(s) than vinylchloride and vinyl acetate as main comonomers constituting the copolymerinclude vinyl alcohol and vinyl alcohol derivatives, such as vinylpropionate; acrylic and methacrylic acid and derivatives thereof, suchas methyl, ethyl, propyl, butyl, and 2-ethylhexyl esters of acrylic andmethacrylic acids; maleic acid and derivatives thereof, such as diethylmaleate, dibutyl maleate, and dioctyl maleate; derivatives of vinylether, such as methyl vinyl ether, butyl vinyl ether, and 2-ethylhexylvinyl ether; acrylonitrile; methacrylonitrile; and styrene. The contentsof the vinyl chloride and vinyl acetate in the copolymer are notparticularly limited. However, the content of vinyl chloride in thecopolymer is preferably not less than 50% by weight. The content of thecomponents other than vinyl chloride and vinyl acetate is preferably notmore than 10% by weight.

The average degree of polymerization of the copolymer comprising theabove comonomers should be 800 to 2000. In the case of vinylchloride/vinyl acetate copolymers having an average degree ofpolymerization of less than 800, for example, the above commerciallyavailable vinyl chloride/vinyl acetate copolymers having an averagedegree of polymerization of 200 to 700, the image-receiving layer haspoor resistance to roughening in the high-energy print area thereof orto scratch. On the other hand, copolymers having an average degree ofpolymerization exceeding 2000 have poor solubility in various solvents,and, hence, the solid content of a coating liquid cannot be made high,or the coating liquid becomes highly viscous, rendering the coatingdifficult.

In the thermal transfer image-receiving sheet according to the presentinvention, the image-receiving sheet may be formed of a mixture of theabove vinyl chloride/vinyl acetate copolymer having a high degree ofpolymerization with other thermoplastic resin(s). Thermoplastic resinsusable herein include polyolefin resins such as polypropylene;halogenated polymers such as polyvinyl chloride and polyvinylidenechloride; vinyl resins such as polyvinyl acetate, ethylene/vinyl acetatecopolymer, and polyacrylic esters; polyester resins; polystyrene resins;polyamide resins; olefin/vinyl monomer copolymer resins; ionomers;cellulosic resins such as cellulose diacetate; polycarbonate resins;polyvinyl acetal resins; and polyvinyl alcohol resins. When the mixtureof the vinyl chloride/vinyl acetate copolymer having a high degree ofpolymerization with the above resin is used, the content of the vinylchloride/vinyl acetate copolymer having a high degree of polymerizationin the mixture is not less than 50% by weight.

If necessary, various other additives may be added. For example, arelease agent may be added so that the thermal transfer sheet and thethermal transfer image-receiving sheet are not heat-fused to each otherat the time of printing. Reaction-curable silicones, such asvinyl-modified silicone, amino-modified silicone, and epoxy-modifiedsilicone, may be mentioned as particularly preferred release agents. Theamount of the release agent added is preferably 0.5 to 10% by weightbased on the resin.

Further, a plasticizer may be added in order to improve the sensitivityof the image-receiving layer. Plasticizers usable herein include thosecommonly used in vinyl chloride resin, for example, monomericplasticizers, such as phthalic esters, phosphoric esters, adipic esters,and sebacic esters, and polyester plasticizers prepared by polymerizingadipic acid or sebacic acid with propylene glycol. In general, theplasticizers listed above have a low molecular weight. In addition,special olefin copolymer resins as a high-molecular plasticizer forvinyl chloride may also be used. Resins usable herein include thosecommercially available under the trade name designations Elvaloy 741,Elvaloy 742, Elvaloy HP 443, Elvaloy HP 553, Elvaloy EP 4015, Elvaloy EP4043, and Elvaloy EP 4051 (manufactured by Du Pont-Mitsui PolychemicalsCo., Ltd.). The amount of the above plasticizer added may be up to about100% by weight based on the resin. However, it is preferably not morethan 30% by weight from the viewpoint of bleeding of the print.

Further, in order to impart an antistatic property, it is also possibleto incorporate the following antistatic agent into a coating liquid foran image-receiving layer: fatty acid esters, sulfuric esters, phosphoricesters, amides, quaternary ammonium salts, betaine, amino acids, acrylicresins, ethylene oxide adducts and the like.

The amount of the antistatic agent added is preferably 0.1 to 2.0% byweight based on the resin.

The image-receiving layer may be formed by adding the above optionaladditives and the like to the above vinyl chloride/vinyl acetatecopolymer as a main component, thoroughly kneading them in a solvent, adiluent or the like to prepare a coating liquid for an image-receivinglayer, coating the coating liquid onto the above substrate sheet, forexample, by gravure printing, screen printing, or reverse roll coatingusing a gravure plate, and drying the coating to form an image-receivinglayer.

In the thermal transfer image-receiving sheet according to the presentinvention, the coating liquid for an image-receiving layer shouldpreferably be coated at a coverage of 0.5 to 4.0 g/m² on a dry weightbasis. When the coverage is less than 0.5 g/mg² on a dry weight basis,for example, when an image-receiving layer is provided directly on thesubstrate, the adhesion of the image-receiving layer to the thermal headis likely to be unsatisfactory due to the rigidity of the substrate orthe like, posing a problem of harsh image in its highlight area. Thisproblem can be avoided by providing an intermediate layer for impartinga cushioning property. This means, however, deteriorates the scratchresistance of the image-receiving layer.

There is a tendency that the surface roughening resistance of theimage-receiving layer upon the application of high energy decreasesrelatively with increasing the coverage of the image-receiving layer.When the coverage exceeds 4.0 g/m² on a dry weight basis, thehigh-density area projected through OHP is sometimes slightly blackish.

<Intermediate layer>

In the thermal transfer image-receiving sheet according to the presentinvention, an intermediate layer formed of various resins may beprovided between the substrate sheet and the image-receiving layer.Excellent functions may be added to the image-receiving sheet byimparting various properties to the intermediate layer.

For example, a resin having large elastic deformation or plasticdeformation, for example, a polyolefin, vinyl copolymer, polyurethane,or polyamide resin, may be used as a resin for imparting a cushioningproperty in order to improve the sensitivity of the image-receivingsheet or to prevent harsh image. Further, when the intermediate layer isprovided using a resin having a glass transition temperature of 60° C.or above or a resin which has been cured with a curing agent or thelike, the adhesion between sheets can be prevented when a plurality ofsheets of the image-receiving sheet are stored with the sheets being puton top of one another, thereby improving the storage stability of theimage-receiving sheet.

When an antistatic property is imparted to the intermediate layer, theintermediate layer may be prepared by dissolving or dispersing the aboveresin, with an antistatic resin or a resin having an antistatic propertyadded thereto, in a solvent and coating the solution or the dispersionto form an intermediate layer.

Antistatic agents usable herein include, for example, fatty acid esters,sulfuric esters, phosphoric esters, amides, quaternary ammonium salts,betaine, amino acids, acrylic resins, and ethylene oxide adducts.

Resins having an antistatic property usable herein include, for example,conductive resins prepared by introducing a group having an antistaticeffect, such as a quaternary ammonium salt, phosphoric acid,ethosulfate, vinyl pyrrolidone, or sulfonic acid group, into a resin,such as an acrylic, vinyl, or cellulose resin, or alternatively bycopolymerizing the above resin with the above group having an antistaticeffect. A cation-modified acrylic resin is particularly preferred.

Preferably, the group having an antistatic effect is introduced in apendant form into the resin from the viewpoint of introducing the groupat a high density. Specific examples of commercially availableantistatic resins include Jurymer series manufactured by Nihon JunyakuCo., Ltd., Reolex series manufactured by Dai-Ichi Kogyo Seiyaku Co.,Ltd., and Elecond series manufactured by Soken Chemical Engineering Co.,Ltd.

The intermediate layer may be formed by thoroughly kneading the aboveresin with optional additives in a solvent, a diluent or the like toprepare a coating liquid for an intermediate layer, coating the coatingliquid onto the above substrate sheet by the same means as describedabove in connection with the formation of the image-receiving layer,that is, such as gravure printing, screen printing, or reverse rollcoating using a gravure plate, and drying the coating to form anintermediate layer.

<Back side layer>

A back side layer may be provided on the back side of the substratesheet for purposes of improvement in carriability of the thermaltransfer image-receiving sheet, prevention of curling of the sheet, orother purposes. The back side layer having such a function may be formedof an acrylic resin with an organic filler, such as a fluororesin or apolyamide resin.

Preferably, the back side layer is formed of a composition containing anacrylic polyol and fine particles of an organic material.

Acrylic polyols usable herein include polymers, such as ethylene glycolmethacrylate and propylene glycol methacrylate. Further, acrylic polyolswherein the ethylene glycol moiety is trimethylene glycol, butanediol,pentanediol, hexanediol, cyclopentanediol, cyclohexanediol, or glycerinmay also be used. The acrylic polyol contributes to prevention ofcurling, can hold additives such as organic or inorganic fillers, andhas good adhesion to the substrate.

More preferably, the back side layer is formed of a cured productprepared by curing an acrylic polyol with a curing agent. The curingagent may be a generally known one. Among others, the use of anisocyanate compound is preferred. The reaction of the acrylic polyolwith an isocyanate compound results in the formation of a urethane bondto cure the acrylic polyol, thereby forming a stereostructure to improvethe heat resistance, the storage stability, and the solvent resistance.Further, it can and to improve the adhesion of the back side layer tothe substrate. The amount of the curing agent added is preferably 1 to 2equivalents based on one reactive group equivalent of the resin.

Further, the addition of an organic filler to the back side layer ispreferred. The filler functions to improve the carriability of the sheetwithin a printer and, at the same time, to prevent blocking or the like,thereby improving the storage stability of the sheet. Organic fillersusable herein include acrylic fillers, polyamide fillers, fluorofillers,and polyethylene wax. Among them, polyamide fillers are particularlypreferred. Preferably, the polyamide filler has a molecular weight of100,000 to 900,000 and are spherical with an average particle diameterof 0.01 to 10 μm. The polyamide filler has a high melting point, isstable against heat, has good oil resistance and chemical resistance,and is less likely to be dyed with a dye. Further, when the polyamidefiller has a molecular weight of 100,000 to 900,000, it is hardlyabraded, has a self-lubricating property and a low coefficient offriction, and is less likely to damage a counter material with which theback side layer is brought into friction. In the polyamide filler, nylon12 filler is better than nylon 6 and nylon 66 fillers because it hassuperior water resistance and is free from any property changeattributable to water absorption.

The amount of the filler added is preferably 0.05 to 200% by weightbased on the resin. In this connection, it should be noted that, in thecase of an image-receiving sheet, for OHP, wherein the addition of afiller deteriorates transparency of the sheet, the filler is added in anamount of not more than 2% by weight based on the resin, or a fillerhaving a small particle diameter is selected.

The provision of the above back side layer can improve the scratchresistance of the image-receiving layer of the thermal transferimage-receiving sheet according to the present invention.

The back side layer may be prepared by thoroughly kneading the aboveresin with an organic filler in a solvent, a diluent or the like toprepare a coating liquid for a back side layer, coating the coatingliquid onto the surface of the substrate sheet, remote from theimage-receiving layer, by the same means as described above inconnection with the formation of the image-receiving layer, that is,such as gravure printing, screen printing, or reverse roll coating usinga gravure plate, and drying the coating to form a back side layer.

<Adhesive layer>

An adhesive layer formed of an adhesive resin, such as an acrylic esterresin, a polyurethane resin, or a polyester resin, may be provided on atleast one side of the substrate sheet.

The adhesive layer may be prepared by preparing a coating liquid usingthe above resin, coating the coating liquid on at least one side of thesubstrate sheet, for example, by gravure printing, screen printing, orreverse roll coating using a gravure plate, and drying the coating toform an adhesive layer.

Alternatively, at least one side of the substrate sheet may be subjectedto corona discharge treatment without providing the above coating,thereby enhancing the adhesion of the substrate sheet to a layerprovided on the substrate sheet.

<Antistatic layer>An antistatic layer may be provided on at least oneside of the substrate sheet, on the image-receiving surface or the backside of the image-receiving sheet, or on the outermost surface of eachof both sides of the image-receiving sheet. The antistatic layer may beformed by dissolving or dispersing an antistatic agent, for example, afatty acid ester, a sulfuric ester, a phosphoric ester, an amide, aquaternary ammonium salt, betaine, an amino acid, an acrylic resin, oran ethylene oxide adduct, in a solvent, coating the solution ordispersion, and drying the coating.

In this case, the dispersion or the solution may be coated, for example,by gravure printing, screen printing, or reverse roll coating using agravure plate. The coverage is preferably 0.001 g/m² to 0.1 g/m² on adry weight basis.

Since an image-receiving sheet having an antistatic layer on theoutermost surface thereof has an antistatic property before printing, itcan prevent feed troubles such as double feed. Further, troubles such asdropout caused by attraction of dust or the like can be prevented.

As described above, by virtue of the provision of an image-receivinglayer, comprising a copolymer, having an average degree ofpolymerization of 800 to 2000, of at least vinyl chloride and vinylacetate as main comonomers, the resin on the surface of theimage-receiving layer is less likely to be roughened by heat applied bymeans of a thermal head at the time of high energy printing, preventingonly a high density area from being matted or preventing the formationof a blackish projected image in the case of an image-receiving sheetfor OHP.

Further, since the resin constituting the surface of the image-receivingsheet comprises a copolymer, having an average degree of polymerizationof 800 to 2000, of at least vinyl chloride and vinyl acetate as maincomonomers and is less likely to be subjected to elastic or plasticdeformation, the image-receiving layer is less likely to be scratched.

The following examples further illustrate the present invention but arenot intended to limit it. In the following examples and comparativeexamples, all "parts" or "%" are by weight unless otherwise specified.

EXAMPLE 1

A coating liquid, for an intermediate layer, having the followingcomposition was coated on the following substrate A by gravure coatingat a coverage on a dry basis of 0.7 g/m², and the coating was dried toform an intermediate layer. A coating liquid A, for an image-receivinglayer, having the following composition was coated on the intermediatelayer by roll coating at a coverage on a dry basis of 3.0 g/m², and thecoating was dried to form an image-receiving layer. A coating liquid A,for a back side layer, having the following composition was then coatedon the back side of the substrate remote from the image-receiving layerby roll coating at a coverage on a dry basis of 4.0 g/m², and thecoating was dried to form a back side layer. Finally, a coating liquid,for an antistatic layer, having the following composition was coated onthe image-receiving layer and on the back side layer by roll coatingeach at a coverage on a dry basis of 0.01 g/m², and the coatings werethen dried to form an antistatic layer on each of the image-receivinglayer and the back side layer, thereby preparing an image-receivingsheet of Example 1.

Substrate A

A 125 μm-thick transparent polyethylene terephthalate (PET) sheet bothsides of which have been subjected to antistatic treatment (LumirrorU-94, manufactured by Toray Industries, Inc.)

    ______________________________________                                        Coating liquid for intermediate layer                                         Antistatic resin (cation-modified                                                                      10     parts                                         acrylic resin)(Elecond PQ-50B                                                 manufactured by Soken Chemical                                                Engineering Co., Ltd.)                                                        Toluene                  15     parts                                         Methyl ethyl ketone      15     parts                                         Coating liquid A for image-receiving layer                                    Vinyl chloride/vinyl acetate                                                                           100    parts                                         copolymer resin: degree of                                                    polymerization = 930                                                          (vinyl chloride: 83%/vinyl acetate: 17%)                                      Vinyl-modified silicone: X-62-1212                                                                     2      parts                                         (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Catalyst: PL-50T         1      part                                          (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Solvent: MEK/toluene = 1/1                                                                             600    parts                                         (weight ratio)                                                                Coating liquid A for back side layer                                          Acrylic polyol resin: Acrydic 47-538                                                                   300    parts                                         (manufactured by Dainippon Ink                                                and Chemicals, Inc.)                                                          Isocyanate curing agent: Takenate A-14                                                                 30     parts                                         (manufactured by Takeda Chemical                                              Industries, Ltd.)                                                             Fine particles of polyamide: MW-330                                                                    1      part                                          (manufactured by Shinto Paint Co., Ltd.)                                      Catalyst: S-CAT 24 (manufactured by                                                                    1      part                                          Sankyo Organic Chemicals Co., Ltd.)                                           Solvent: MEK/toluene/butyl acetate =                                                                   700    parts                                         3/3/1 (weight ratio)                                                          Coating liquid for antistatic layer                                           Antistatic agent: TB-34  0.1    part                                          (manufactured by Matsumoto                                                    Yushi Seiyaku Co., Ltd.)                                                      Solvent: IPA             200    parts                                         ______________________________________                                    

EXAMPLE 2

An image-receiving sheet of Example 2 was prepared in the same manner asin Example 1, except that a coating liquid B, for an image-receivinglayer, having the following composition was used instead of the coatingliquid A for an image-receiving layer.

    ______________________________________                                        Coating liquid B for image-receiving layer                                    ______________________________________                                        Vinyl chloride/vinyl acetate                                                                           100    parts                                         copolymer resin: degree of                                                    polymerization = 1500                                                         (vinyl chloride: 75%/vinyl acetate: 25%)                                      Amino-modified silicone: KF-393                                                                        1.5    parts                                         (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Epoxy-modified silicone: X-22-343                                                                      1.5    parts                                         (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Solvent: MEK/toluene = 1/1                                                                             600    parts                                         (weight ratio)                                                                ______________________________________                                    

EXAMPLE 3

An image-receiving sheet of Example 3 was prepared in the same manner asin Example 1, except that a coating liquid C, for an image-receivinglayer, having the following composition was used instead of the coatingliquid A for an image-receiving layer.

    ______________________________________                                        Coating liquid C for image-receiving layer                                    ______________________________________                                        Vinyl chloride/vinyl acetate                                                                          80     parts                                          copolymer resin: degree of                                                    polymerization = 1200                                                         (vinyl chloride: 90%/vinyl acetate: 3%/                                       PVA: 7%)                                                                      Polyester resin: Vylon 600                                                                            20     parts                                          (manufactured by Toyobo Co., Ltd.)                                            Vinyl-modified silicone: X-62-1212                                                                    3      parts                                          (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Catalyst: PL-50T        1.5    parts                                          (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Solvent: MEK/toluene = 1/1                                                                            600    parts                                          (weight ratio)                                                                ______________________________________                                    

EXAMPLE 4

An image-receiving sheet of Example 4 was prepared in the same manner asin Example 1, except that a coating liquid D, for an image-receivinglayer, having the following composition was used instead of the coatingliquid A for an image-receiving layer.

    ______________________________________                                        Coating liquid D for image-receiving layer                                    ______________________________________                                        Vinyl chloride/vinyl acetate                                                                          100    parts                                          copolymer resin: degree of                                                    polymerization = 1050                                                         (vinyl chloride: 85%/vinyl acetate: 14%/                                      maleic acid: 1%)                                                              Vinyl-modified silicone: X-62-1212                                                                    3      parts                                          (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Catalyst: PL-50T        1.5    parts                                          (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Solvent: MEK/toluene = 1/1                                                                            600    parts                                          (weight ratio)                                                                ______________________________________                                    

EXAMPLE 5

An image-receiving sheet of Example 5 was prepared in the same manner asin Example 1, except that a coating liquid E, for an image-receivinglayer, having the following composition was used instead of the coatingliquid A for an image-receiving layer.

    ______________________________________                                        Coating liquid E for image-receiving layer                                    ______________________________________                                        Vinyl chloride/vinyl acetate                                                                           100    parts                                         copolymer resin: degree of                                                    polymerization = 930                                                          (vinyl chloride: 83%/vinyl acetate: 17%)                                      Plasticizer: DOP         12     Parts                                         Vinyl modified silicone: X-62-1212                                                                     3      parts                                         (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Catalyst: PL-50T         1.5    parts                                         (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Solvent: MEK/toluene = 1/1                                                                             600    parts                                         (weight ratio)                                                                ______________________________________                                    

EXAMPLE 6

An image-receiving sheet of Example 6 was prepared in the same manner asin Example 1, except that a coating liquid F, for an image-receivinglayer, having the following composition was used instead of the coatingliquid A for an image-receiving layer.

    ______________________________________                                        Coating liquid F for image-receiving layer                                    ______________________________________                                        Vinyl chloride/vinyl acetate                                                                           100    parts                                         copolymer resin: degree of                                                    polymerization = 930                                                          (vinyl chloride: 83%/vinyl acetate: 17%)                                      Polymeric plasticizer: Elvaloy 741                                                                     20     parts                                         (manufactured by Du Pont-Mitsui                                               Polychemicals Co., Ltd.)                                                      Vinyl-modified silicone: X-62-1212                                                                     2      parts                                         (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Catalyst: PL-50T         1      part                                          (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Solvent: MEK/toluene = 1/1                                                                             600    parts                                         (weight ratio)                                                                ______________________________________                                    

EXAMPLE 7

An image-receiving sheet of Example 7 was prepared in the same manner asin Example 1, except that a coating liquid G, for an image-receivinglayer, having the following composition was used instead of the coatingliquid A for an image-receiving layer.

    ______________________________________                                        Coating liquid G for image-receiving layer                                    ______________________________________                                        Vinyl chloride/vinyl acetate                                                                           70     parts                                         copolymer resin: degree of                                                    polymerization = 930                                                          (vinyl chloride: 83%/vinyl acetate: 17%)                                      Vinyl chloride/vinyl acetate                                                                           30     parts                                         copolymer resin: degree of                                                    polymerization = 420                                                          #1000 AKT (manufactured by Denki Kagaku                                       Kogyo K.K.)                                                                   (vinyl chloride: 83%/vinyl acetate: 17%)                                      Vinyl modified silicone: X-62-1212                                                                     2      parts                                         (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Catalyst: PL-50T         1      part                                          (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Solvent: MEK/toluene = 1/1                                                                             600    parts                                         (weight ratio)                                                                ______________________________________                                    

EXAMPLE 8

An image-receiving sheet of Example 8 was prepared in the same manner asin Example 1, except that the following substrate B was used instead ofthe substrate A.

Substrate B

A 100 μm-thick white PET sheet both sides of which have been subjectedto antistatic treatment (Lumirror E-22, manufactured by TorayIndustries, Inc.)

EXAMPLE 9

An image-receiving sheet of Example 9 was prepared in the same manner asin Example 6, except that the substrate B as used in Example 8 was usedinstead of the substrate A.

EXAMPLE 10

An image-receiving sheet of Example 10 was prepared in the same manneras in Example 1, except that a coating liquid B, for a back side layer,having the following composition was used instead of the coating liquidA for a back side layer.

    ______________________________________                                        Coating liquid B for back side layer                                          ______________________________________                                        Acrylic resin: Dianal BR-85                                                                            200    parts                                         (manufactured by Mitsubishi                                                   Rayon Co., Ltd.)                                                              Fine particles of fluororesin:                                                                         1      part                                          Ruburon L-5                                                                   (manufactured by Daikin Industries, Ltd.)                                     Solvent: MEK/toluene = 1/1                                                                             800    parts                                         (weight ratio)                                                                ______________________________________                                    

EXAMPLE 11

An image-receiving sheet of Example 11 was prepared in the same manneras in Example 1, except that the image-receiving layer was provided at acoverage on a dry weight basis of 5.0 g/m².

EXAMPLE 12

An image-receiving sheet of Example 12 was prepared in the same manneras in Example 7, except that the coating liquid B, for a back sidelayer, as used in Example 10 was used instead of the coating liquid Afor a back side layer.

Comparative Example 1

An image-receiving sheet of Comparative Example 1 was prepared in thesame manner as in Example 1, except that a coating liquid H, for animage-receiving layer, having the following composition was used insteadof the coating liquid A for an image-receiving layer.

    ______________________________________                                        Coating liquid H for image-receiving layer                                    ______________________________________                                        Vinyl chloride/vinyl acetate                                                                           100    parts                                         copolymer resin: degree of                                                    polymerization = 690                                                          #1000 MT2 (manufactured by Denki Kagaku                                       Kogyo K.K.)                                                                   (vinyl chloride: 80%/vinyl acetate: 20%)                                      Vinyl modified silicone: X-62-1212                                                                     2      parts                                         (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Catalyst: PL-50T         1      part                                          (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Solvent: MEK/toluene = 1/1                                                                             600    parts                                         (weight ratio)                                                                ______________________________________                                    

Comparative Example 2

An image-receiving sheet of Comparative Example 2 was prepared in thesame manner as in Example 1, except that a coating liquid H, for animage-receiving layer, having the following composition was used insteadof the coating liquid A for an image-receiving layer.

    ______________________________________                                        Coating liquid I for image-receiving layer                                    ______________________________________                                        Vinyl chloride/vinyl acetate                                                                           100    parts                                         copolymer resin: degree of                                                    polymerization = 420                                                          #1000 AKT (manufactured by Denki Kagaku                                       Kogyo K.K.)                                                                   (vinyl chloride: 83%/vinyl acetate: 17%)                                      Vinyl modified silicone: X-62-1212                                                                     2      parts                                         (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Catalyst: PL-50T         1      part                                          (manufactured by Shin-Etsu                                                    Chemical Co., Ltd.)                                                           Solvent: MEK/toluene = 1/1                                                                             600    parts                                         (weight ratio)                                                                ______________________________________                                    

Comparative Example 3

An image-receiving sheet of Comparative Example 3 was prepared in thesame manner as in Comparative Example 1, except that the substrate B asused in Example 8 was used instead of the substrate A.

Comparative Example 4

An image-receiving sheet of Comparative Example 4 was prepared in thesame manner as in Comparative Example 2, except that the substrate B asused in Example 8 was used instead of the substrate A.

Each of the thermal transfer image-receiving sheets prepared in theexamples and the comparative examples and a commercially availablesublimation thermal transfer sheet were put on top of the other so thatthe image-receiving layer faced the dye layer, and heating was carriedout from the back side of the thermal transfer sheet by means of athermal head.

Evaluation of roughening resistance of surface of image-receiving layer

A printer which is equipped with a 300-dpi thermal head and can conductregulation of 256 gradations was provided. A 16-step pattern withequally divided 256 gradation values (ranging from 0 to 255) wasprepared, using this printer, for each color of yellow, magenta, andcyan and black formed by overprinting three colors of yellow, magenta,and cyan. The printing was carried out under conditions of printingspeed 10 ms/line and maximum applied thermal energy 0.65 mJ/dot in the16th step image. The resistance to roughening was evaluated for the 16thstep image of each color of yellow, magenta, and cyan and black formedby overprinting of three colors of yellow, magenta, and cyan. When thesubstrate used was transparent, the print was projected through OHP andthe projected image was visually inspected for the darkening of theimage. On the other hand, when the substrate used was white, the printwas visually inspected for matting of the high-density area.

Evaluation criteria are as follows.

⊚: Neither blackening nor matting of image observed for each color.

◯: Blackening of image not observed in projection through OHP, althoughmatting of image observed for only black formed by overprinting of thethree colors.

Δ: Matting of image observed for each color, and slight blackening ofimage observed in projection through OHP.

x: Matting of image observed in the near 15th and 16th step images, andblacking of image observed in projection through OHP.

Evaluation of scratch resistance of image-receiving surface

A plurality of sheets for each thermal transfer image-receiving sheetprepared in the examples and the comparative examples were set in asheet cassette and automatically fed one by one into a printer wherehalftone solid printing was performed thereon.

The plurality of sheets of the image-receiving sheet, which are put ontop of one another within the sheet cassette, are fed one by one bymeans of a pickup roll into the printer. For example, when the pluralityof sheets of the image-receiving sheet are set with the image-receivingsurface downward, friction occurs between the image-receiving surface ofthe image-receiving sheet pressed by the pickup roll and the back sideof the image-receiving sheet located beneath the pressed sheet, oftencausing the sheet in its portion in contact with the pickup roll to bescratched. The releasability of the scratched portion often becomesunsatisfactory, resulting in abnormal transfer. In the test, the sheetswere visually inspected for scratch. Among the sheets put on top of oneanother, a sheet located at the uppermost position and a sheet locatedat the lowermost position were not evaluated. The evaluation criteriaare as follows.

⊚: Scratch hardly observed by visual inspection.

◯: Slight scratch, having no influence on projection of the imagethrough OHP, observed by visual inspection.

Δ: No abnormal transfer observed despite the presence of scratchobservable by visual inspection.

x: Scratch observed by visual inspection, and abnormal transfer observedin the scratched portion.

Results of evaluation

For the image-receiving sheets prepared in the examples and thecomparative examples, the layer construction is shown in Table 1, andthe results of evaluation are tabulated in Table 2.

                  TABLE 1                                                         ______________________________________                                                        Coverage                                                               Image- (g/m.sup.2)        Back                                                receiving                                                                            (dry weight Sub-   side                                                layer  basis)      strate layer                                      ______________________________________                                        Example 1  A        3           A    A                                        2          B        3           A    A                                        3          C        3           A    A                                        4          D        3           A    A                                        5          E        3           A    A                                        6          F        3           A    A                                        7          G        3           A    A                                        8          A        3           B    A                                        9          F        3           B    A                                        10         A        3           A    B                                        11         A        5           A    A                                        12         G        3           A    B                                        Comparative                                                                   Example 1  H        3           A    A                                        2          I        3           A    A                                        3          H        3           B    A                                        4          I        3           B    A                                        ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                                     Roughening                                                                            Scratch                                                               resistance                                                                            resistance                                               ______________________________________                                        Example 1      ⊚                                                                        ⊚                                     2              ⊚                                                                        ⊚                                     3              ∘                                                                           ⊚                                     4              ⊚                                                                        ⊚                                     5              ∘                                                                           ∘                                        6              ⊚                                                                        ∘                                        7              ∘                                                                           ⊚                                     8              ⊚                                                                        ⊚                                     9              ⊚                                                                        ∘                                        10             ⊚                                                                        ∘                                        11             Δ   ⊚                                     12             ∘                                                                           Δ                                              Comparative                                                                   Example 1      Δ   Δ                                              2              x         x                                                    3              Δ   Δ                                              4              x         x                                                    ______________________________________                                    

A comparison of the results of Examples 1 to 10 with those ofComparative Examples 3 to 6 reveals that the image-receiving layer usinga vinyl chloride/vinyl acetate copolymer having a high degree ofpolymerization offered better roughening resistance and scratchresistance than the image-receiving layer using a vinyl chloride/vinylacetate copolymer having a relatively low degree of polymerization.Further, a comparison of the results of Example 1 with those of Example11 reveals that increasing the coverage of the image-receiving layerresulted in increased tendency of roughening. Furthermore, a comparisonof the results of Example 7 with those of Example 12 reveals that theback side layer not containing a combination of an acrylic polyol withfine particles of an organic material had scratch resistance inferior tothe back side layer containing an acrylic polyol in combination withfine particles of an organic material. Thus, it was found that not onlythe use of a vinyl chloride/vinyl acetate copolymer having a high degreeof polymerization but also coating of the image-receiving layer at acoverage on a dry weight basis of 0.5 to 4 g/m² and the provision of aback side layer containing an acrylic polyol in combination with fineparticles of an organic material are effective in providing animage-receiving layer having high resistance to roughening and scratch.

What is claimed is:
 1. A thermal transfer image-receiving sheetcomprising: a substrate sheet; and an image-receiving layer provided onone side of the substrate sheet, the image-receiving layer comprising acopolymer, having an average degree of polymerization of 930 to 2000, ofat least vinyl chloride and vinyl acetate as main comonomers.
 2. Thethermal transfer image-receiving sheet according to claim 1, wherein thecoverage of the image-receiving layer is 0.5 to 4.0 g/m² on a dry weightbasis.
 3. The thermal transfer image-receiving sheet according to claim1, which further comprises a back side layer provided on the other sideof the substrate sheet, the back side layer being formed of acomposition comprising an acrylic polyol and fine particles of anorganic material.
 4. The thermal transfer image-receiving sheetaccording to claim 1, which further comprises an intermediate layer,having an antistatic property, between the substrate sheet and theimage-receiving layer.
 5. The thermal transfer image-receiving sheetaccording to claim 1, wherein the substrate sheet is a transparentsheet.
 6. The thermal transfer image-receiving sheet according to claim1, wherein at least one side of the substrate sheet has been subjectedto adhesiveness-improving treatment or antistatic treatment.